Alloys or metallic compositions – Processes
Patent
1987-01-28
1988-05-17
Brody, Christopher W.
Alloys or metallic compositions
Processes
148430, 148432, C22C 900
Patent
active
047449470
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to a method of dispersion-hardening of copper, silver or gold, as well as of their alloys, as matrix metal with metal borides as dispersoid. In addition, the invention relates to the application of this method to the production of any spot welding electrodes, in particular for welding galvanized sheets.
The known methods of dispersion-hardening of copper, silver or gold either start from extremely fine and thus very expensive powders of the matrix metal which is thoroughly mixed with the dispersoid, mostly aluminum oxide or beryllium oxide particles, and subsequently compacted and extruded; or alloys of the matrix metal containing small proportions of easily oxidizable metals such as beryllium or aluminum are processed into powders which are subjected to internal oxidation in a second, expensive and complicated step which, upon appropriate control of the process leads to the desired fine distribution of oxide particles of less than 0.1 .mu.m diameter in a matrix. The method of internal oxidation has the disadvantage that the oxidation is accompanied by external oxidation of copper. This requires final reduction annealing with hydrogen, which in turn leads to undesirable caking of the powders and thus to impaired handling properties, in particular in the production of shaped parts.
Both methods are expensive and complicated and therefore have found only limited acceptance. Simultaneous precipitation of matrix metal and dispersoid from respective metallic salt solutions, as well, is too expensive for application on an industrial scale. In addition, all metals dispersion-hardened with oxides of this type, such as copper or silver, show strong hot embrittlement of about 500.degree. C. The high ductility at room temperature, which is indicated by an ultimate elongation of about 20%, decreases very strongly with increasing temperature to reach a minimum as low as about 2% at about 500.degree. C. This represents a serious disadvantage of these dispersion-hardened alloys.
The object of the invention is to provide a simple and economical method of producing dispersion-hardened alloys on the basis of copper, silver or gold which contain dispersoids that keep hot embrittlement at a minimum.
According to the invention, this object is reached by the fact that melts on the basis of the matrix metals with stoichiometric additions of boron and boride-forming metals are superheated by 300.degree. to 750.degree. C. and subsequently subjected to extremely rapid solidification at a rate of at least 10.sup.3 .degree. to 10.sup.4 .degree. C. per second. Advantegeous embodiments of the method according to the invention are described in claims 2 to 9. Claim 10 relates to the application of the method to the production of spot welding electrodes, in particular for welding galvanized sheets.
Suitable dispersoids are borides of the elements of the groups IV A, V A and VI A of the periodic system, either singly or in combination. Preferably, however, high-melting-point titanium or zirconium boride is formed, together with the mixed boride of titanium and zirconium of the composition Ti.sub.x Zr.sub.1-x B.sub.2. These borides are found to be soluble in the melt to an extent that is sufficient for dispersion hardening, at temperatures of the melt above about 1500.degree. C., and to precipitate in the matrix after extremely rapid solidification, e.g. by atomization, as dispersoid of a particle size below 0.1 .mu.m. It is thus possible to produce dispersion-hardened alloys economically in one step direct from the melt.
To produce dispersion-hardened alloys on the basis of copper, silver or gold according to the invention, their melts are carefully deoxidized and then stoichiometric proportions of boron, titanium and/or zirconium in the form of master alloys are added to form 1 to 5 volume percent of the diboride. The melts are superheated by 300.degree. to 750.degree. C. and subsequently processed into powder at solidification rates of more than 10.sup.3 to 10.sup.4 .degree. C. per second, e.g. by atomi
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Chemical Abstracts, Band 76, No. 8, 21 (1972).
Nilmen Fehmi
Winter Heinrich
Battelle-Institut e.V.
Brody Christopher W.
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